Work Fluctuations and Stochastic Resonance

We study Brownian particle motion in a double-well potential driven by an ac force. This system exhibits the phenomenon of stochastic resonance. Distribution of work done on the system over a drive period in the time asymptotic regime have been calculated. We show that fluctuations in the input energy or work done dominate the mean value. The mean value of work done over a period as a function of noise strength can also be used to characterise stochastic resonance in the system. We also discuss the validity of steady state fluctuation theorems in this particular system.Comment: 5 page

Spectral ageing analysis of the double-double radio galaxy J1453+3308

We present new radio observations at frequencies ranging from 240 to 4860 MHz of the well-known, double-double radio galaxy (DDRG), J1453+3308, using both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). These observations enable us to determine the spectra of the inner and outer lobes over a large frequency range and demonstrate that while the spectrum of the outer lobes exhibits significant curvature, that of the inner lobes appears practically straight. The break frequency, and hence the inferred synchrotron age of the outer structure, determined from 16$-$arcsec strips transverse to the source axis, increases with distance from the heads of the lobes. The maximum spectral ages for the northern and southern lobes are $\sim$47 and 58 Myr respectively. Because of the difference in the lengths of the lobes these ages imply a mean separation velocity of the heads of the lobes from the emitting plasma of 0.036c for both the northern and southern lobes. The synchrotron age of the inner double is about 2 Myr which implies an advance velocity of $\sim$0.1c, but these values have large uncertainties because the spectrum is practically straight.Comment: 10 pages, 10 figures, 5 tables, accepted for publication in MNRA

Cultivar Variation for Capsaicinoid Content in some Processed Products of Chilli

Determination of capsaicinoids content in various products from seven chilli cultivars was made. Capsaicin, the major element among capsaicinoids, is found primarily in the fruit of Capsicum to which it provides spicy flavor. Extraction of capsaicin in the present study was done using acetonitrile as the solvent, and High Performance Liquid Chromatography was used for its quantification. Whole dried-fruits of 'Bhut Red' (Capsicum chinense) showed the highest concentration of capsaicin (2.59%) and level of pungency (4,40,000 SHU), whereas, salted mash of 'Lemon Drop' (Capsicum baccatum) had the lowest capsaicin concentration (0.07%) and pungency level (12,000 SHU). As capsaicinoids are important in food and pharmaceutical industries, developing products from selected cultivars of chilli with high pungency and high capsaicinoid content will prove useful in order to ensuring health security

Tale of J1328+2752 : a misaligned double-double radio galaxy hosted by a binary black-hole?

We present a radio and optical study of the double-double radio galaxy J1328+2752 based on new low-frequency Giant Metrewave Radio Telescope observations and Sloan Digital Sky Survey (SDSS) data. The radio data were used to investigate the morphology and to perform a spectral index analysis. In this source, we find that the inner double is misaligned by similar to 30 degrees from the axis of the outer diffuse structure. The SDSS spectrum shows that the central component has double-peaked line profiles with different emission strengths. The average velocity offset of the two components is 235 +/- 10.5 kms(-1). The misaligned radio morphology along with the double-peaked emission lines indicate that this source is a potential candidate binary supermassive black hole. This study further supports mergers as a possible explanation for repeated jet activity in radio sources

The Dynamics of Radio Galaxies and Double-Double Radio Galaxies

Relativistic and magnetised plasma ejected by radio loud AGNs through jets form the diffuse lobes of radio galaxies. The radiating particles (electron/electron-positron) in lobes emit in radio via the synchrotron process and X-ray via inverse-Compton scattering of cosmic microwave background photons. The thermal environment around radio galaxies emits X-rays via the thermal bremsstrahlung process. By combining information from these processes we can measure physical conditions in and around the radio lobes and thus study the dynamics of radio galaxies, including double-double radio galaxies.Comment: 11 pages, 4 figures, Diffuse Radio Plasma Conference proceedings (held in Raman Research Institute, Bangalore, India

Discovery of a red quasar with recurrent activity

We report a new double-double radio quasar, DDRQ, J0746$+$4526 which exhibits two cycles of episodic activity. From radio continuum observations at 607 MHz using the GMRT and 1400 MHz from the FIRST survey we confirm its episodic nature. We examine the SDSS optical spectrum and estimate the black hole mass to be (8.2$\pm$0.3)$\times$10$^7$M$_\odot$ from its observed MgII emission line, and the Eddington ratio to be 0.03. The black hole mass is significantly smaller than for the other reported DDRQ, J0935+0204, while the Eddington ratios are comparable. The SDSS spectrum is significantly red continuum dominated suggesting that it is highly obscured with ${E(B-V)}_{host}=0.70\pm0.16$ mag. This high obscuration further indicates the existence of a large quantity of dust and gas along the line of sight, which may have a key role in triggering the recurrent jet activity in such objects.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Ap

Relativistic and slowing down: the flow in the hotspots of powerful radio galaxies and quasars

Pairs of radio emitting jets with lengths up to several hundred kiloparsecs emanate from the central region (the `core') of radio loud active galaxies. In the most powerful of them, these jets terminate in the `hotspots', compact high brightness regions, where the jet flow collides with the intergalactic medium (IGM). Although it has long been established that in their inner ($\sim$parsec) regions these jet flows are relativistic, it is still not clear if they remain so at their largest (hundreds of kiloparsec) scales. We argue that the X-ray, optical and radio data of the hotspots, despite their at-first-sight disparate properties, can be unified in a scheme involving a relativistic flow upstream of the hotspot that decelerates to the sub-relativistic speed of its inferred advance through the IGM and viewed at different angles to its direction of motion. This scheme, besides providing an account of the hotspot spectral properties with jet orientation, it also suggests that the large-scale jets remain relativistic all the way to the hotspots.Comment: to appear in ApJ

A low-frequency study of recently identified double-double radio galaxies

In order to understand the possible mechanisms of recurrent jet activity in radio galaxies and quasars, which are still unclear, we have identified such sources with a large range of linear sizes (220 $-$ 917 kpc), and hence time scales of episodic activity. Here we present high-sensitivity 607-MHz Giant Metrewave Radio Telescope (GMRT) images of 21 possible double-double radio galaxies (DDRGs) identified from the FIRST survey to confirm their episodic nature. These GMRT observations show that none of the inner compact components suspected to be hot-spots of the inner doubles are cores having a flat radio spectrum, confirming the episodic nature of these radio sources. We have indentified a new DDRG with a candidate quasar, and have estimated the upper spectral age limits for eight sources which showed marginal evidence of steepening at higher frequencies. The estimated age limits (11 $-$ 52 Myr) are smaller than those of the large-sized ($\sim$ 1 Mpc) DDRGs.Comment: Accepted for publication in MNRAS. 14 pages, 7 figure

Variability and polarization in the inner jet of 3C395

We present new results on the parsec-scale jet of the quasar 3C395, derived from VLBI polarization sensitive observations made in 1995.91 and 1998.50 at 8.4, 15.4 and 22.2 GHz. The observations show a complex one-sided jet extending up to 20 mas, with a projected magnetic field essentially aligned with the radio jet. The emission is strongly dominated, in total intensity and polarization, by the core and the inner jet region (of ~3 mas length). We have studied the details of this dominant region finding clear structural variations during this ~2.5 years period, in contrast with the apparent quietness of the jet structure inferred from lower resolution VLBI observations. We observe the ejection of a new component from the core and variations in the degree of polarization of the inner jet components. We estimate a high Faraday Rotation Measure close to the core, with a strong decrease along the inner jet.Comment: 7 pages, 4 figures, A&A in pres